The general problem is to provide a device capable of transmitting in a secured manner a set of high visual quality films in an MPEG type format (MPEG-1, MPEG-2) directly to a television screen and/or to be recorded on the hard disk of a box connecting the remote transmission network to the television screen, while preserving the audiovisual quality, but preventing fraudulent use such as the possibility of making pirate copies of films or audiovisual programs recorded on the hard disk of the decoder box.
With the presently available solutions, it is possible to transmit films and audiovisual programs in digital form via broadcast networks of the airwaves, cable, satellite, etc. type or via DSL (Digital Subscriber Line) type telecommunication networks or LRL (local radio loop) network or via DAB (Digital Audio Broadcasting) networks. Moreover, in order to prevent pirating of works broadcast in this manner, these works are often encrypted by various means well known to the expert in the field.
However, the principal disadvantage of all of the presently available solutions (TiVo Inc., WO 00/165762) is that it is necessary to transmit not only the encrypted data to the users but also the decryption keys. Transmission of the decryption keys can be performed prior to, at the same time as or after transmission of the audiovisual programs. In order to increase the security and thus the protection of the audiovisual works against ill-intentioned use, the decryption keys as well as the decryption functions of the audiovisual decoders can comprise enhanced security means such as smart cards or other physical keys that can optionally be updated remotely.
Thus, the presently available solutions applied to a decoder box with the ability of local recording of audiovisual programs in digital form on a support of any type such as a hard disk or other type of memory provides an ill-intentioned user the possibility of making unauthorized copies of the programs recorded in this manner because at any given moment the user has with a digital decoder box associated or not with smart card systems all of the information, software programs and data enabling the complete decryption of the audiovisual programs. Precisely because of the fact that the user possesses all of the data, the ill-intentioned user would have the possibility of making illegal copies without anybody becoming aware of this fraudulent copying when it is performed.
One solution would therefore consist of transmitting all or part of a digital audiovisual program solely on demand (on demand video services) via a broad-band telecommunication network of the DSL, cable or satellite type without authorizing the local recording of the audiovisual programs. The disadvantage is completely different and stems from the performances of these networks which do not make it possible to guarantee continuous flows of several megabits per second to each user as required by MPEG flows which require pass bands from several hundreds of kilobits to many megabits per second.
Under these conditions, one solution consists of separating the flow into two parts neither of which could be used by itself. For example, WO 09/908428 discloses a method for the multiapplication processing of a localizable active terminal in which there is implemented at least one link with an identifiable program dedicated to the execution of an application, said program dictating its conditions of exploitation to the terminal for the setting up of its functions. The terminal dialogues in a punctiform manner by using a link with the management center for the implementation, if necessary, of the inputs and outputs of the capacities of this center with the management center optionally becoming the slave of the terminal at the application level in relation to the incoming program. WO '428 also pertains to method for the identification of the program and the terminal in exploitation mode. That method divides the flow into a part used for identifying the user and a part that contains the actual program itself. In particular, said program is not unusable but merely made inaccessible by the first part.
In addition, EP 0778513 describes a method enabling prevention of illegal use of an information unit by adding to it a control information unit to verify the rights of the user. The system makes it possible to remain permanently informed as to which part of the information unit is used and by which user and thereby to be informed as to whether or not this user is in an illegal position. This method thus makes the data secure by adding additional information units which distort the initial information.
WO 00/49483 also discloses methods and systems for creating a link between the users and an editor of digitized entities. The method comprises at least one of the following steps: subdividing the digitized entity into two parts; storing one part in memory in a server connected to a computer-based network; transmitting the other part to at least one user who has available computer-based equipment; connecting the computer-based equipment to the computer-based network; establishing a functional link between the first part and the second part. These methods and systems do not specify whether the part stored in memory on the server can be stored by the user, which would enable the user to pirate the digitized entity.
U.S. Pat. No. 5,937,164 discloses a solution comprised of separating the flow into two parts, the smaller one of which holds an information unit required for the use of the larger part. This patent nevertheless is not sufficient for resolving the identified problem. In fact, suppression of a part of the flow distorts the format of the flow which then cannot be recognized as a standard flow that can be exploited with general software applications. This method of the prior art requires both a specific software program at the server side for the separation of the two parts, and another specific software program enabling not only the reconstruction of the flow, but also the acquisition of the principal flow and its exploitation according to a format proprietary to the solution. This proprietary format is not the initial format of the flow prior to separation into two parts in this known solution.
U.S. Pat. No. 5,892,825 returns to the approach of the preceding patents but in a narrower framework because the flows are still encrypted. U.S. Pat. No. 6,035,329 is based on the same principle and pertains to a method enabling the reading of a DC-ROM or DVD-ROM disk contingent on the identification of the rights by the insertion of a smart card on which the information required for reading are stored. That method is still not adequate because it does not ensure that the modified flow is of the same format as the original flow. U.S. Pat. No. 6,185,306 pertains to a method for the transmission of encrypted data from a Web site to a requesting computer. That method, however, makes it possible for the user to have available at a given moment the tools required for copying the data.
EP 1 011 269 discloses a system for processing an information signal. The object is to prevent the illicit distribution of compressed copies of information flow, especially audio, video and image. The conventional information flow protection systems are generally based on an encryption or scrambling performed on an already compressed and formatted copy of the flow (e.g., encryption of an already compressed DVD, etc.). Thus, the decrypted content of the flow for these conventional protection systems is in decompressed form and thus can be directly exploited and distributed. That system commences by encrypting or scrambling the flow, then compressing it (rather than first compressing then scrambling). In order to achieve this, that system comprises an analysis of the entropy of the flow which makes it possible to scramble the uncompressed flow while still preserving its entropy. Preserving its entropy makes it possible to attain the same compression efficacy for the flow. Scrambling consists of adding noise (of the pseudorandom white noise type) to the signal. This noise is generated by means of a scrambling key. This key is then encrypted by a single user via a public key-private key system, the private key employed being specific to the unscrambling system of the intended client. The scrambling key encrypted in this manner is then sent to the client possessing viewing rights at the same time as the protected flow. At the client end, the flow is decompressed, then an unscrambling signal is added to it (substrate) which is obtained by means of the unscrambling key provided to the client. In the case of video, that system applies to the DCT coefficients of each image prior to their compression (by VLC, etc.). Only the I images are scrambled because otherwise the other images of the MPEG flow would correct the following images, then it would be necessary to scramble all of the images. In the case of a DVD, for example, at the location, the point of sale gives to the client a diskette (or other medium) containing the unscrambling key corresponding to the client.
EP 0 975 165 discloses a device and a method for transmitting from a transmitter to a receiver signals the access to which is controlled. EP '165 pertains to the management of the copying and viewing rights of a video flow. It enables the transmission by two separate paths of two flows containing the video and the access control information. The video flow received in the client's device is, in a first implementation, unscrambled then optionally encrypted by a system based on public and private keys. If the user has all of the rights to the film, the user can freely copy it and watch it as desired. If the user only has the rights to one or a limited number of viewings, the flow copied on the client's equipment on a cassette or a CD or other medium will have been encrypted in advance. When the flow in question is viewed, it is decrypted by a decrypter contained in the client's equipment. If the user no longer has rights, the encrypted flow that was copied or is in the process of being read is not decrypted because the access control module does not authorize the decryption. The client access controls are managed and processed by an access control module that is internal in the client's equipment. The access control data are saved on the cassette or CD/DVD on which the video is recorded. They moreover can be downloaded. In another implementation, the same method is used but the access control module does not control an encrypter/decrypter pair integrated in the client's equipment but the unscrambler which unscrambles the video flow received by the video server.
WO 00/60846 discloses an on-demand video distribution solution via a system of distributed servers. Protection of the content of the digital video is based on public/private keys. The principal innovation of WO '846 is to enable a simplified encryption and decryption of the MPEG-TS flows. The calculation time is in fact greatly diminished thanks to an analysis of the MPEG-TS flow which makes it possible to not encrypt certain parts of the content. This flow analysis consists principally of marking the TS packets containing an information unit that is essential for the correct decoding (in the MPEG sense) of the video such that in a second encrypting phase only the marked TS packet payloads are not encrypted. Thus the essential information is not available for decoding and the flow thus cannot be displayed while still preserving a reasonable calculation time for encryption. It is then necessary to transmit in the flow the information enabling the decrypter to know whether or not the payload of a packet is encrypted. This can be done in various ways such as, for example, adding an info before the synchronization byte or by modification of the scrambling control bit or of an info of the adaptation field. The packets generated in this manner do not conform perfectly to the standard.